JP6667142B2 - Storage element - Google Patents

Description

  The present invention relates to a power storage device such as a lithium ion secondary battery.

  Conventionally, a lithium ion secondary battery including a negative electrode and an electrolyte, wherein the negative electrode has a current collector and a negative electrode material layer formed on the current collector and containing a negative electrode active material, Is known (for example, Patent Document 1).

  In the battery described in Patent Literature 1, when the negative electrode material layer is divided in half in the thickness direction and the negative electrode material layer on the current collector side is A1 and the negative electrode material layer on the opposite side to the current collector side is A2, The average porosity of A1 is higher than the average porosity of A2.

  In the battery described in Patent Literature 1, the difference in the amount of discharged electricity between the high rate and the low rate may be large, and the difference in the amount of discharged electricity between the high rate and the low rate is suppressed from increasing. There is a need for a storage element.

JP 2003-077542 A

  An object of the present embodiment is to provide a power storage element in which a difference in the amount of discharge electricity between a high rate and a low rate is suppressed.

  The power storage element of the present embodiment includes an electrode body having a positive electrode and a negative electrode as electrodes, and an electrolytic solution.The electrode body has a separator base material disposed between the positive electrode and the negative electrode. Has an active material layer containing active material particles, the active material layer of the positive electrode and the active material layer of the negative electrode face each other with a separator substrate interposed therebetween, and at least a gap in the active material layer of any one of the electrodes. The ratio is different between one side and the other in the thickness direction, and one side closer to the separator substrate is lower than the other, and the electrode body has a higher porosity than the separator substrate and an activity having a different porosity. It further has a high void layer disposed between the material layer and the separator substrate. In such a configuration, in the other portion of the active material layer where the porosity is high, there is a large amount of electrolyte solution that has entered the voids due to the high porosity. On the other hand, the electrolyte solution is easily supplied from the high void layer to one part of the active material layer where the porosity is low. As a result, the active material layer is impregnated with a sufficient amount of the electrolytic solution that contributes to the discharge reaction. Accordingly, the discharge reaction easily proceeds at a high rate or a low rate, and a sufficient amount of electricity can be discharged at any time. Therefore, it is possible to provide a power storage element in which the difference in the amount of discharged electricity between the high rate and the low rate is suppressed.

  In the above power storage device, the one porosity near the separator base material may be 38% or more. According to such a configuration, the difference in the amount of discharge electricity between the high rate and the low rate is further suppressed.

  In the above power storage device, each of the positive electrode and the negative electrode has an active material layer in which the porosity is lower in one direction than the other in the thickness direction, and the high void layer is formed by the active material layer of the positive electrode and the separator base material. It may be disposed both between the active material layer of the negative electrode and the separator base material. According to such a configuration, the difference in the amount of discharge electricity between the high rate and the low rate is further suppressed.

  According to the present embodiment, it is possible to provide a power storage element in which the difference in the amount of discharge electricity between the high rate and the low rate is suppressed.

FIG. 1 is a perspective view of a power storage device according to the present embodiment. FIG. 2 is a sectional view taken along the line II-II in FIG. FIG. 3 is a sectional view taken along line III-III in FIG. FIG. 4 is a diagram for explaining the configuration of the electrode body of the power storage device according to the embodiment. FIG. 5 is a cross-sectional view (a VV cross section in FIG. 4) of the superposed positive electrode, negative electrode, and separator. FIG. 6 is a cross-sectional view schematically illustrating an electrode, a high void layer, and a separator substrate. FIG. 7 is a perspective view of a power storage device including the power storage element according to the same embodiment.

  Hereinafter, an embodiment of a power storage device according to the present invention will be described with reference to FIGS. 1 to 6. The storage element includes a primary battery, a secondary battery, a capacitor, and the like. In this embodiment, a chargeable / dischargeable secondary battery is described as an example of a power storage element. The names of the components (components) in the present embodiment are those in the present embodiment, and may be different from the names of the components (components) in the background art.

  The electric storage element 1 of the present embodiment is a non-aqueous electrolyte secondary battery. More specifically, power storage element 1 is a lithium ion secondary battery that utilizes electron transfer that occurs with the movement of lithium ions. This type of storage element 1 supplies electric energy. The storage element 1 is used singly or in plural. Specifically, the storage element 1 is used alone when the required output and the required voltage are small. On the other hand, when at least one of the required output and the required voltage is large, power storage element 1 is used in power storage device 100 in combination with another power storage element 1. In the power storage device 100, the power storage element 1 used in the power storage device 100 supplies electric energy.

  As shown in FIGS. 1 to 6, the electric storage element 1 includes an electrode body 2 including a positive electrode 11 and a negative electrode 12, a case 3 for housing the electrode body 2, and an external terminal 7 arranged outside the case 3. And an external terminal 7 electrically connected to the electrode body 2. In addition, the power storage element 1 includes a current collector 5 that conducts the electrode body 2 and the external terminal 7, in addition to the electrode body 2, the case 3, and the external terminal 7.

  The electrode body 2 is formed by winding a laminate 22 in which the positive electrode 11 and the negative electrode 12 are laminated while being insulated from each other by the separator 4 (separator substrate 41). The electrode body 2 preferably has a high void layer 8 having a higher porosity than the separator substrate 41 between the positive electrode or the negative electrode 12 and the separator substrate 41.

  The positive electrode 11 includes a metal foil 111 (a current collector foil) and a positive electrode active material layer 112 that is stacked on the surface of the metal foil 111 and contains an active material. In the present embodiment, the positive electrode active material layers 112 respectively overlap on both surfaces of the metal foil 111. In addition, the thickness of the positive electrode 11 is usually 40 μm or more and 150 μm or less.

  The metal foil 111 has a band shape. The metal foil 111 of the positive electrode 11 of the present embodiment is, for example, an aluminum foil. The positive electrode 11 has an uncovered portion (a portion where the positive electrode active material layer is not formed) 115 of the positive electrode active material layer 112 at one edge in the width direction, which is the short direction of the belt shape. The metal foil 111 may have a through hole penetrating in the thickness direction.

The positive electrode active material layer 112 contains a particulate active material (active material particles), a particulate conductive auxiliary, and a binder. The thickness of the positive electrode active material layer 112 (for one layer) is usually 12 μm or more and 70 μm or less. The basis weight of the positive electrode active material layer 112 (for one layer) is usually 6 mg / cm ² or more and 17 mg / cm ² or less. The density of the positive electrode active material layer 112 is usually 1.0 g / cm ³ or more and 6.0 g / cm ³ or less. The basis weight and the density are for one layer arranged to cover one surface of the metal foil 111.

  The porosity of the positive electrode active material layer 112 may be different between one and the other in the thickness direction. Specifically, the porosity of the positive electrode active material layer 112 is lower on the side closer to the separator base material 41 (one) and higher on the side closer to the metal foil 111 (the other side). That is, the porosity of the positive electrode active material layer 112 is higher in a portion closer to the metal foil 111 (a portion farther from the separator substrate 41) than in a portion closer to the separator substrate 41. As shown in FIG. 6, for example, the positive electrode active material layer 112 is formed porous by gaps between the plurality of active material particles A. The area ratio of such a gap per unit area of the cross section of the active material layer is lower on the side closer to the separator substrate 41 (one side). The difference in the porosity in the thickness direction is confirmed by comparing the porosity of one and the other when the thickness of the positive electrode active material layer 112 is reduced to half. Specifically, it is as follows. First, the battery in the discharged state is disassembled in a dry atmosphere. A part of the positive electrode 11 is cut out from the disassembled battery, the active material layer 112 of the positive electrode 11 is washed with dimethyl carbonate, and then vacuum dried for 2 hours or more. In a scanning electron microscope (SEM) observation of a cross section of the dried positive electrode 11 in which the positive electrode active material layer 112 is cut in the thickness direction, a square having four sides each having a half length of the thickness of the positive electrode active material layer 112 is observed. Set the image. The observation images are set for one and the other in the thickness direction. By calculating the ratio of the area occupied by the voids to the total area of the observed image, the respective porosity is determined.

  In the positive electrode active material layer 112, the porosity closer to the metal foil 111 may be higher than the porosity closer to the separator substrate 41 by 3 to 5 points. The porosity of the positive electrode active material layer 112 closer to the metal foil 111 is usually 35% or more and 50% or less. On the other hand, the porosity near the separator substrate 41 is usually 25% or more and 45% or less. The porosity near the separator substrate 41 may be 35% or more, or may be 38% or more.

  The porosity of the positive electrode active material layer 112 is made different in the thickness direction by, for example, applying a mixture (described later) for forming the positive electrode active material layer 112 a plurality of times to produce the positive electrode active material layer 112. be able to. Specifically, after applying a mixture having a lower solid content to the metal foil 111, by further applying a mixture having a higher solid content, the closer to the metal foil 111 than the closer to the separator substrate 41 is. Thus, the positive electrode active material layer 112 having a high porosity can be manufactured. Further, for example, after a mixture for forming the positive electrode active material layer 112 is applied to the metal foil 111 once, the mixture is subjected to a drying treatment at a relatively high temperature, and the metal foil 111 side and the surface side are mixed. And a method of causing a difference in porosity between the two. Thereby, the positive electrode active material layer 112 having a higher porosity can be manufactured closer to the metal foil 111 than to the separator base material 41.

  The active material of the positive electrode 11 is a compound capable of inserting and extracting lithium ions. The average primary particle diameter of the active material of the positive electrode 11 is usually 0.5 μm or more and 2.0 μm or less. The average primary particle size is measured as described below. The positive electrode 11 is cut in the thickness direction, and a cross section of the positive electrode active material layer 112 that appears by the cutting is observed with a scanning electron microscope. Primary particles of at least 100 active material particles are randomly selected in a cross section. The particle size of the selected primary particles is measured and averaged. When the active material particles are not truly spherical, the longest diameter is measured.

The active material of the positive electrode 11 is, for example, a lithium metal oxide. Specifically, the active material of the positive electrode, for _example, Li p _MeO t (Me represents one or more transition metal) complex oxide represented by _{(Li p Co s O 2,} Li p Ni q O _2, a _{Li p Mn r O 4, Li} p Ni q Co s Mn r O 2 , etc.).

More specifically, the active material of the positive electrode _{11, Li p Ni q Mn r Co} s O lithium-metal composite oxide represented by the chemical composition of the _t (where a 0 <p ≦ 1.3, q + r + s = 1 And 0 ≦ q ≦ 1, 0 ≦ r ≦ 1, 0 ≦ s ≦ 1, and 1.7 ≦ t ≦ 2.3). Note that 0 <q <1, 0 <r <1, and 0 <s <1.

Additional such _{Li p Ni q Mn r Co s} O lithium-metal composite oxide represented by the chemical composition of the _t, for _{example, LiNi 1/3 Co 1/3 Mn 1/3 O} 2, LiNi 1/6 Co 1 _{/ 6} Mn _2/3 O ₂ , LiCoO ₂ and the like. At this time, the lithium metal composite oxide may contain trace elements other than those indicated by the chemical composition.

  The binder used for the positive electrode active material layer 112 is, for example, polyvinylidene fluoride (PVdF), a copolymer of ethylene and vinyl alcohol, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic Acid, styrene butadiene rubber (SBR). The binder of the present embodiment is polyvinylidene fluoride.

  The positive electrode active material layer 112 contains a carbonaceous material containing 98% by mass or more of carbon as a conductive additive. The positive electrode active material layer 112 may contain, for example, Ketjen Black (registered trademark), acetylene black, graphite, or the like as a conductive additive.

  The negative electrode 12 includes a metal foil 121 (a current collecting foil) and a negative electrode active material layer 122 formed on the metal foil 121. In the present embodiment, the negative electrode active material layers 122 are respectively stacked on both surfaces of the metal foil 121. The metal foil 121 has a band shape. The metal foil 121 of the negative electrode of the present embodiment is, for example, a copper foil. The negative electrode 12 has a non-covered portion (a portion where the negative electrode active material layer is not formed) 125 of the negative electrode active material layer 122 at one edge in the width direction, which is a short direction of the band shape. The thickness of the negative electrode 12 is usually 40 μm or more and 150 μm or less.

  The negative electrode active material layer 122 includes a particulate active material (active material particles) and a binder. The negative electrode active material layer 122 is disposed so as to face the positive electrode active material layer 112 via the separator 4 (separator substrate 41). The width of the negative electrode active material layer 122 is larger than the width of the positive electrode active material layer 112.

  The active material of the negative electrode 12 can contribute to an electrode reaction of a charging reaction and a discharging reaction in the negative electrode 12. For example, the active material of the anode 12 is a graphite such as natural graphite or artificial graphite, a carbon material such as amorphous carbon (hardly graphitized carbon, easily graphitized carbon), or silicon (Si) and tin (Sn). It is a material that causes an alloying reaction with lithium ions. The active material of the negative electrode of the present embodiment is graphite, specifically, natural graphite.

The thickness of the negative electrode active material layer 122 (for one layer) is usually 10 μm or more and 50 μm or less. The basis weight (for one layer) of the negative electrode active material layer 122 is usually 0.3 g / 100 cm ² or more and 1.0 g / 100 cm ² or less. The density (for one layer) of the negative electrode active material layer 122 is usually 0.5 g / cm ³ or more and 6.0 g / cm ³ or less.

  The porosity of the negative electrode active material layer 122 may be different in the thickness direction, similarly to the positive electrode active material layer 112. Specifically, the porosity of the negative electrode active material layer 122 may be lower near the separator substrate 41 and higher near the metal foil 121. That is, the porosity of the negative electrode active material layer 122 may be higher in a portion closer to the metal foil 121 than in a portion closer to the separator substrate 41. The porosity of the negative electrode active material layer 122 is measured in the same manner as the porosity of the positive electrode active material layer 112 described above.

  The binder used for the negative electrode active material layer is the same as the binder used for the positive electrode active material layer. The binder of the present embodiment is styrene butadiene rubber (SBR).

  In the negative electrode active material layer 122, the ratio of the binder may be 1% by mass or more and 10% by mass or less with respect to the total mass of the active material particles and the binder.

  The negative electrode active material layer 122 may further include a conductive additive such as Ketjen Black (registered trademark), acetylene black, graphite, or the like. The negative electrode active material layer 122 of this embodiment does not have a conductive auxiliary.

  In the electrode body 2 of the present embodiment, the positive electrode 11 and the negative electrode 12 configured as described above are wound while being insulated by the separator 4 (separator substrate 41). That is, in the electrode body 2 of the present embodiment, the laminate 22 of the positive electrode 11, the negative electrode 12, and the separator 4 is wound. The separator 4 is a member having an insulating property. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12. Thereby, in the electrode body 2 (specifically, the laminated body 22), the positive electrode 11 and the negative electrode 12 are insulated from each other. The separator 4 holds the electrolytic solution in the case 3. Thereby, at the time of charging / discharging of the storage element 1, lithium ions move between the positive electrode 11 and the negative electrode 12, which are alternately stacked with the separator 4 interposed therebetween.

  The separator 4 has a band shape. The separator 4 has a porous separator substrate 41. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12 to prevent a short circuit between the positive electrode 11 and the negative electrode 12. The separator 4 of the present embodiment has only the separator base material 41. The porosity of the separator substrate 41 is higher than the porosity of the positive electrode active material layer 112 closer to the metal foil 111, and is usually 40% or more and 70% or less.

  The porosity of the separator substrate 41 is determined by using a part of the separator 4 cut out from the battery disassembled at the time of the measurement in the same manner as in the above-described method for measuring the porosity of the positive electrode active material layer 112, using a scanning electron microscope. Obtained from observation images. The porosity of the separator substrate 41 can be changed, for example, by employing the separator substrates 41 having different air resistances.

  The separator substrate 41 is configured to be porous. The separator substrate 41 is, for example, a woven fabric, a nonwoven fabric, or a porous film. Examples of the material of the separator substrate include a polymer compound, glass, and ceramic. Examples of the polymer compound include a group consisting of polyester such as polyacrylonitrile (PAN), polyamide (PA) and polyethylene terephthalate (PET), polyolefin (PO) such as polypropylene (PP) and polyethylene (PE), and cellulose. At least one selected from the following is included.

  The electrode body 2 of the present embodiment has the high void layer 8 disposed between the positive electrode active material layer 112 or the negative electrode active material layer 122 and the separator substrate 41. The electrode body 2 may have the high void layer 8 both between the positive electrode active material layer 112 and the separator substrate 41 and between the negative electrode active material layer 122 and the separator substrate 41. The porosity of the negative electrode active material layer 122 may be different in the thickness direction, like the porosity of the positive electrode active material layer 112 described above. The porosity of the high void layer 8 is higher than the porosity of the separator substrate 41. The porosity of the high void layer 8 is higher than the porosity of the positive electrode active material layer 112 (or the negative electrode active material layer 122) closer to the separator base material 41, and is closer to the metal foil 111 (or the metal foil 121). Higher than porosity. The porosity of the high void layer 8 is usually 55% or more and 85% or less.

  The porosity of the high porosity layer 8 is determined by using a part of the high porosity layer 8 cut out of the battery disassembled at the time of the measurement in the same manner as in the above-described method of measuring the porosity of the positive electrode active material layer 112. It is determined from the observation image of the microscope. The porosity of the high void layer 8 can be determined, for example, by reducing the amount of the inorganic particles and the binder (described later) in the composition containing the solvent, which is prepared for forming the high void layer 8, by reducing the solid content. , Can be higher.

The high void layer 8 includes at least inorganic particles having electrical insulation properties, and further includes a binder. The electrical insulation of the high void layer 8 is higher than that of any of the positive electrode active material layer 112 and the negative electrode active material layer 122. The electrical conductivity of the high void layer 8 is less than 10 ⁻⁶ S / m.

The high void layer 8 is formed porous by voids between the inorganic particles so that Li ions and the like can move between the positive electrode 11 and the negative electrode 12. The inorganic particles contain at least 95% by mass of an insulating material having an electric conductivity of less than 10 ⁻⁶ S / m.

  The high void layer 8 usually contains 30% by mass or more and 99% by mass or less of inorganic particles. The high void layer 8 usually contains 1% by mass or more and 70% by mass or less of a binder.

Examples of the inorganic particles include oxide particles, nitride particles, ionic crystal particles, covalent crystal particles, clay particles, mineral resource-derived substances, and particles of artificial substances thereof. Examples of the oxide particles (metal oxide particles) include particles such as iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₂ , ZrO, and alumina-silica composite oxide. Examples of the nitride particles include particles such as aluminum nitride and silicon nitride. Examples of the ion crystal particles include particles of calcium fluoride, barium fluoride, barium sulfate, and the like. Examples of the particles of the covalent crystal include particles of silicon, diamond, and the like. Examples of the clay particles include particles such as talc and montmorillonite. Examples of the particles of the mineral resources-derived material or their artificial materials include particles of boehmite (alumina hydrate), zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, and the like. In addition, a fired body obtained by firing a natural mineral containing a hydrate (for example, the above-mentioned clay, a substance derived from a mineral resource) can also be used. In the present embodiment, the inorganic particles are Al ₂ O ₃ particles.

  The binder of the high void layer 8 is, for example, polyacrylonitrile, polyvinylidene fluoride (PVdF), a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, or polyphophate. Examples include sphazene, polysiloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, and polycarbonate.

  The high void layer 8 is formed between the separator substrate 41 and the positive electrode active material layer 112 or the negative electrode active material layer 122 by being formed on the surface of the positive electrode active material layer 112 or the negative electrode active material layer 122. Is also good. Further, the high void layer 8 may be disposed between the separator substrate 41 and the positive electrode active material layer 112 or the negative electrode active material layer 122 by being formed on the surface of the separator substrate 41.

  The width of the separator 4 (the dimension in the width direction of the strip) is slightly larger than the width of the negative electrode active material layer 122. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12 that are superposed with the positive electrode active material layer 112 and the negative electrode active material layer 122 displaced in the width direction so as to overlap. At this time, as shown in FIG. 4, the uncovered portion 115 of the positive electrode 11 and the uncovered portion 125 of the negative electrode 12 do not overlap. That is, the uncovered portion 115 of the positive electrode 11 protrudes in the width direction from the region where the positive electrode 11 and the negative electrode 12 overlap, and the uncovered portion 125 of the negative electrode 12 extends in the width direction (from the region where the positive electrode 11 and the negative electrode 12 overlap). (The direction opposite to the direction in which the uncovered portion 115 of the positive electrode 11 protrudes). The electrode body 2 is formed by winding the stacked positive electrode 11, negative electrode 12, and separator 4, that is, the stacked body 22. The uncoated laminated portion 26 of the electrode body 2 is configured by a portion where only the uncoated portion 115 of the positive electrode 11 or the uncoated portion 125 of the negative electrode 12 is laminated.

  The uncoated laminated portion 26 is a portion that is electrically connected to the current collector 5 in the electrode body 2. The uncoated laminated portion 26 has two portions (a two-part uncoated laminated portion) sandwiching the hollow portion 27 (see FIG. 4) as viewed in the winding center direction of the wound positive electrode 11, negative electrode 12, and separator 4. ) 261.

  The uncoated laminated portion 26 configured as described above is provided on each pole of the electrode body 2. That is, the uncoated laminated portion 26 in which only the uncoated portion 115 of the positive electrode 11 is laminated constitutes the uncoated laminated portion of the positive electrode 11 in the electrode body 2, and the uncoated laminated portion in which only the uncoated portion 125 of the negative electrode 12 is laminated. The part 26 constitutes the uncoated laminated part of the negative electrode 12 in the electrode body 2.

  The case 3 includes a case body 31 having an opening, and a cover plate 32 that closes (closes) the opening of the case body 31. The case 3 accommodates the electrolytic solution in the internal space together with the electrode body 2 and the current collector 5 and the like. Case 3 is formed of a metal having resistance to the electrolytic solution. The case 3 is formed of, for example, aluminum or an aluminum-based metal material such as an aluminum alloy. The case 3 may be formed of a metal material such as stainless steel and nickel, or a composite material obtained by bonding a resin such as nylon to aluminum.

The electrolyte is a non-aqueous electrolyte. The electrolyte is obtained by dissolving an electrolyte salt in an organic solvent. Organic solvents are, for example, cyclic carbonates such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. The electrolyte salt is LiClO ₄ , LiBF ₄ , LiPF ₆ or the like. The electrolytic solution of the present embodiment is obtained by dissolving 0.5 to 1.5 mol / L of LiPF ₆ in a mixed solvent in which propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a predetermined ratio.

  The case 3 is formed by joining the peripheral edge of the opening of the case main body 31 and the peripheral edge of the rectangular lid plate 32 in an overlapping state. The case 3 has an internal space defined by the case body 31 and the lid plate 32. In the present embodiment, the periphery of the opening of the case body 31 and the periphery of the lid plate 32 are joined by welding.

  Hereinafter, as shown in FIG. 1, the long side direction of the cover plate 32 is defined as the X-axis direction, the short side direction of the cover plate 32 is defined as the Y-axis direction, and the normal direction of the cover plate 32 is defined as the Z-axis direction. The case body 31 has a rectangular cylindrical shape (ie, a bottomed rectangular cylindrical shape) in which one end in the opening direction (Z-axis direction) is closed. The cover plate 32 is a plate-shaped member that closes the opening of the case main body 31.

  The cover plate 32 has a gas discharge valve 321 that can discharge the gas in the case 3 to the outside. The gas discharge valve 321 discharges gas from inside the case 3 to the outside when the internal pressure of the case 3 rises to a predetermined pressure. The gas discharge valve 321 is provided at the center of the cover plate 32 in the X-axis direction.

  The case 3 is provided with an injection hole for injecting the electrolyte. The liquid injection hole communicates the inside and the outside of the case 3. The liquid injection hole is provided in the lid plate 32. The liquid injection hole is sealed (closed) by the liquid injection plug 326. The injection plug 326 is fixed to the case 3 (the cover plate 32 in the example of the present embodiment) by welding.

  The external terminal 7 is a portion that is electrically connected to the external terminal 7 of another power storage element 1 or an external device or the like. The external terminal 7 is formed of a conductive member. For example, the external terminal 7 is formed of a metal material having high weldability, such as an aluminum-based metal material such as aluminum or an aluminum alloy, or a copper-based metal material such as copper or a copper alloy.

  The external terminal 7 has a surface 71 to which a bus bar or the like can be welded. The surface 71 is a plane. The external terminal 7 has a plate shape extending along the cover plate 32. Specifically, the external terminal 7 has a rectangular plate shape when viewed in the Z-axis direction.

  The current collector 5 is arranged in the case 3 and is directly or indirectly connected to the electrode body 2 so as to be able to conduct electricity. The current collector 5 of the present embodiment is electrically connected to the electrode body 2 via the clip member 50. That is, the electric storage element 1 includes the clip member 50 that connects the electrode body 2 and the current collector 5 so as to be able to conduct electricity.

  The current collector 5 is formed of a conductive member. As shown in FIG. 2, current collector 5 is arranged along the inner surface of case 3. Current collector 5 is arranged on each of positive electrode 11 and negative electrode 12 of power storage element 1. In the power storage device 1 of the present embodiment, the current collectors 5 are arranged in the case 3 in the uncoated laminated portion 26 of the positive electrode 11 of the electrode body 2 and the uncoated laminated portion 26 of the negative electrode 12, respectively.

  The current collector 5 of the positive electrode 11 and the current collector 5 of the negative electrode 12 are formed of different materials. Specifically, the current collector 5 of the positive electrode 11 is formed of, for example, aluminum or an aluminum alloy, and the current collector 5 of the negative electrode 12 is formed of, for example, copper or a copper alloy.

  In the power storage element 1 of the present embodiment, the electrode body 2 (specifically, the electrode body 2 and the current collector 5) housed in the bag-shaped insulating cover 6 that insulates the electrode body 2 from the case 3 is the case 3. Housed within.

  Next, a method for manufacturing the power storage device 1 of the above embodiment will be described.

  In the method for manufacturing the power storage device 1, first, a mixture containing an active material is applied to a metal foil (current collector foil) to form an active material layer, and electrodes (the positive electrode 11 and the negative electrode 12) are manufactured. Next, the positive electrode 11, the separator 4, and the negative electrode 12 are overlapped to form the electrode body 2. Subsequently, the electrode body 2 is put in the case 3, and the electrolytic solution is put in the case 3 to assemble the electricity storage device 1.

  In manufacturing the electrode (positive electrode 11), a positive electrode active material layer 112 is formed by applying a mixture containing an active material, a binder, and a solvent to both surfaces of a metal foil. By changing the applied amount of the mixture, the thickness and the basis weight of the positive electrode active material layer 112 can be adjusted. As a coating method for forming the positive electrode active material layer 112, a general method is employed. At this time, after applying a mixture having a lower solid content to the metal foil, by further applying a mixture having a higher solid content, the porosity differs in the thickness direction, and the porosity is closer to the metal foil. Can form an active material layer with a high density. After applying the mixture, the solvent contained in the mixture can be volatilized by heating or the like. When the mixture is applied once, by elevating the temperature at the time of heating, the volatilization rate of the solvent is increased, and an active material layer having a high porosity near the metal foil can be formed. Further, the positive electrode active material layer 112 is roll-pressed at a predetermined pressure. By changing the pressing pressure, the thickness and density of the positive electrode active material layer 112 can be adjusted. Note that, similarly, the negative electrode 12 can be manufactured.

In the formation of the electrode body 2, the electrode body 2 is formed by winding a laminate 22 having the separator 4 interposed between the positive electrode 11 and the negative electrode 12. Specifically, the positive electrode 11, the separator 4, and the negative electrode 12 are overlapped with each other so that the positive electrode active material layer 112 and the negative electrode active material layer 122 face each other with the separator 4 interposed therebetween. The electrode body 2 is formed by winding the laminate 22.
The high void layer 8 is formed, for example, by applying a composition containing inorganic particles, a binder, and a solvent to the surface of the separator substrate 41, or forming at least one of the active material layers of the positive electrode 11 and the negative electrode 12. It can be formed by coating on the surface. Then, when wound as described above, the laminated body 22 on which the high void layer 8 is also laminated is wound.

  In assembling the storage element 1, the electrode body 2 is put in the case main body 31 of the case 3, the opening of the case main body 31 is closed with the cover plate 32, and the electrolytic solution is injected into the case 3. When closing the opening of the case main body 31 with the cover plate 32, the electrode body 2 is put inside the case main body 31, the positive electrode 11 and one external terminal 7 are electrically connected, and the negative electrode 12 and the other external terminal 7 are connected. In the conductive state, the opening of the case body 31 is closed by the cover plate 32. When the electrolyte is injected into the case 3, the electrolyte is injected into the case 3 from an injection hole of the cover plate 32 of the case 3.

  The energy storage device 1 of the present embodiment configured as described above includes the electrode body 2 having the positive electrode 11 and the negative electrode 12 as electrodes, and an electrolytic solution. The electrode body 2 has a separator base material 41 disposed between the positive electrode 11 and the negative electrode 12. The positive electrode 11 and the negative electrode 12 have a positive electrode active material layer 112 and a negative electrode active material layer 122 containing active material particles, respectively. The positive electrode active material layer 112 and the negative electrode active material layer 122 face each other with a separator substrate interposed therebetween. The porosity of the positive electrode active material layer 112 or the negative electrode active material layer 122 is different between the one in the thickness direction and the other, and is lower at the one near the separator substrate 41 than at the other. The electrode body 2 further includes a high void layer 8 having a higher porosity than the separator substrate 41 and disposed between the positive electrode active material layer 112 and the separator substrate 41 having different porosity. In such a configuration, in the other portion of the positive electrode active material layer 112 or the negative electrode active material layer 122 where the porosity is high, a large amount of the electrolyte is present in the voids due to the high porosity. On the other hand, the electrolytic solution is easily supplied to one portion of the positive electrode active material layer 112 or the negative electrode active material layer 122 having a low porosity from the high porosity layer 8 having a relatively high porosity. Thus, the positive electrode active material layer 112 or the negative electrode active material layer 122 is impregnated with a sufficient amount of the electrolytic solution that contributes to the discharge reaction. Therefore, the discharge reaction easily proceeds at a high rate or a low rate, and a sufficient amount of electricity can be discharged at any time. Therefore, it is possible to provide a power storage element in which the difference in the amount of discharged electricity between the high rate and the low rate is suppressed.

  In the above-described power storage device 1, the porosity of the positive electrode active material layer 112 or the negative electrode active material layer 122 closer to (one of) the separator base material 41 may be 38% or more. According to such a configuration, the difference in the amount of discharge electricity between the high rate and the low rate is further suppressed.

  In the above-described power storage device 1, the high void layers 8 are respectively disposed between the positive electrode active material layer 112 and the separator substrate 41 and between the negative electrode active material layer 122 and the separator substrate 41. Is also good. The porosity of each of the positive electrode active material layer 112 and the negative electrode active material layer 122 differs in the thickness direction, and may be lower in a direction farther from the separator base material 41 (the other side) than in a direction farther away (the other side). According to such a configuration, the difference in the amount of discharge electricity between the high rate and the low rate is further suppressed.

  It should be noted that the electric storage device of the present invention is not limited to the above embodiment, and it is needless to say that various changes can be made without departing from the spirit of the present invention. For example, the configuration of another embodiment can be added to the configuration of one embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment. Further, a part of the configuration of an embodiment can be deleted.

  In the above embodiment, the positive electrode in which the active material layer containing the active material is in direct contact with the metal foil has been described in detail. However, in the present invention, the positive electrode is a conductive layer containing a binder and a conductive auxiliary, and the active material layer And a conductive layer disposed between the metal foil and the metal foil.

  In the above embodiment, the electrode in which the active material layer is disposed on both sides of the metal foil of each electrode has been described. However, in the power storage element of the present invention, the positive electrode 11 or the negative electrode 12 is configured such that the active material layer is formed on one side of the metal foil. It may be provided only on the side.

  In the above embodiment, the power storage device 1 including the electrode body 2 formed by winding the laminate 22 has been described in detail. However, the power storage device of the present invention may include the laminate 22 that is not wound. Specifically, the power storage element may include an electrode body in which a positive electrode, a separator, a negative electrode, and a separator each formed in a rectangular shape are stacked a plurality of times in this order.

  In the above embodiment, the case where the power storage element 1 is used as a chargeable / dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described, but the type and size (capacity) of the power storage element 1 are arbitrary. is there. Further, in the above embodiment, the lithium ion secondary battery has been described as an example of the power storage element 1, but the present invention is not limited to this. For example, the present invention can be applied to various secondary batteries, primary batteries, and power storage elements of capacitors such as electric double layer capacitors.

  The power storage device 1 (for example, a battery) may be used for a power storage device 100 (a battery module when the power storage device is a battery) as shown in FIG. Power storage device 100 includes at least two power storage elements 1 and a bus bar member 91 that electrically connects the two (different) power storage elements 1 to each other. In this case, the technology of the present invention only needs to be applied to at least one storage element.

  A non-aqueous electrolyte secondary battery (lithium ion secondary battery) was manufactured as described below.

(Example 1)
(1) Preparation of Positive Electrode N-methyl-2-pyrrolidone (NMP) as an organic solvent, a conductive additive (acetylene black), a binder (PVdF), and active material particles (LiNi _1/3 Co _1/3 Mn) _1/3 O ₂ ) and kneading the mixture to prepare two types of mixes for the positive electrode. First, a low solids mixture was prepared in which the amounts of the conductive auxiliary agent, the binder, and the active material particles were 4.5% by mass, 4.5% by mass, and 91% by mass, respectively. Next, a high-solids mixture was prepared in which the amounts of the conductive auxiliary agent, the binder, and the active material particles were 4.5% by mass, 4.5% by mass, and 91% by mass, respectively. At this time, a mixture having a high solid content was prepared by making the amount of the organic solvent smaller than that of the mixture having a low solid content. The prepared mixture having a low solid content was applied to both surfaces of an aluminum foil (thickness: 15 μm) such that the applied amount after drying (for one layer) was 4.3 mg / cm ² . On the applied mixture, a high-solids mixture was applied so that the applied amount after drying (for one layer) was 4.3 mg / cm ² . After drying, a roll press was performed at a predetermined pressure. Then, it was dried under vacuum to remove moisture and the like. The thickness of the active material layer (for one layer) was 32 μm. The density of the active material layer was 2.69 g / cm ³ .

(2) Preparation of Negative Electrode Natural graphite particles were used as active material particles. Styrene butadiene rubber was used as a binder. The mixture for the negative electrode was prepared by mixing and kneading water as a solvent, a binder, carboxymethyl cellulose (CMC), and active material particles. CMC was blended so as to be 1.0% by mass, binder was blended so as to be 2.0% by mass, and active material particles were blended so as to be 97.0% by mass. The prepared negative electrode mixture was applied to both surfaces of a copper foil (thickness: 10 μm) such that the coating amount after drying (for one layer) was 3.8 mg / cm ² . After drying, a roll press was performed, followed by vacuum drying to remove moisture and the like. The thickness of the active material layer (for one layer) was 39 μm. The density of the active material layer was 0.974 g / cm ³ .

(3) Separator (separator substrate)
A polyethylene microporous membrane having a thickness of 22 μm was used as a separator substrate. The air resistance of the polyethylene microporous membrane was 100 seconds / 100 cc.

(4) High void layer (inorganic porous layer)
A composition containing 95% by mass of inorganic particles (alumina particles), 5% by mass of a binder (specifically, polyvinylidene fluoride) and a solvent was prepared, and the composition was applied to one surface of a separator substrate. . The solvent was evaporated by heating to form a high void layer (inorganic porous layer) on the separator substrate. Before the electrode body was wound as described below, the high void layer was arranged so as to be in contact with the positive electrode active material layer.

(5) Preparation of Electrolyte Solution An electrolyte solution prepared by the following method was used. As a non-aqueous solvent, a solvent in which propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed by 1 volume part was used, and LiPF ₆ was dissolved in this non-aqueous solvent so that the salt concentration was 1 mol / L. An electrolyte was prepared.

(6) Arrangement of electrode body in case A battery was manufactured by a general method using the above positive electrode, the above negative electrode, the above electrolytic solution, a separator, a high void layer, and a case.
First, a sheet formed by laminating a separator between the positive electrode and the negative electrode was wound. Next, the wound electrode body was arranged in a case body of a rectangular battery case made of aluminum as a case. Subsequently, the positive electrode and the negative electrode were electrically connected to the two external terminals, respectively. Further, a lid plate was attached to the case body. The above-mentioned electrolytic solution was injected into the case through a liquid inlet formed in the lid plate of the case. Finally, the case was hermetically closed by sealing the liquid inlet of the case.

(Examples 2 to 15, Comparative Examples 1 to 10)
A battery was manufactured in the same manner as in Example 1, except that the porosity of the positive electrode active material layer, the separator substrate, and the high void layer was changed as shown in Table 1.
Specifically, in Examples 1 to 15 and Comparative Examples 1 to 10 (excluding Comparative Examples 2, 6, and 8), as described above, after applying the low-solids mixture, the high-solids mixture was added. By coating, a positive electrode active material layer having a different porosity in the thickness direction was produced.
On the other hand, in Comparative Examples 2, 6, and 8, the positive electrode active material layer having the same porosity in the thickness direction was produced by applying the mixture of the predetermined solid content only once.
In each example and each comparative example (except for Comparative Examples 1 and 5) shown in Table 1, a high void layer was formed on one surface of the separator substrate.
Further, in each of Examples and Comparative Examples (excluding Comparative Example 7) shown in Table 2, a composition for a high void layer was applied to the surface of the positive electrode active material layer to thereby form the positive electrode active material layer. A high void layer was formed thereon.
Note that none of the negative electrode active material layers was formed so that the porosity in the thickness direction was different.

<Evaluation of the difference (discharge rate characteristic) between the amount of discharge electricity at the high rate and the low rate>
The battery charged to 4.2 V was discharged to 2.4 V at a discharge current of 40 A, and the amount of discharged electricity C1 at the time of discharging at 40 A was measured.
The battery subjected to the above measurement was charged to 4.2 V and discharged to 2.4 V with a discharge current of 200 A, thereby measuring the amount of discharged electricity C2 at the time of discharging 200 A.
Then, the value calculated by the formula [C2 / C1] × 100 was used as the discharge rate characteristic.

  Tables 1 and 2 show the evaluation results of the discharge rate characteristics of the manufactured batteries. As can be seen from Tables 1 and 2, in the batteries of the examples, the increase in the difference in the amount of discharged electricity between the high rate and the low rate was suppressed.

1: storage element (non-aqueous electrolyte secondary battery),
2: electrode body,
26: uncoated laminated part,
3: Case, 31: Case body, 32: Lid plate,
4: separator,
5: current collector, 50: clip member,
6: insulating cover,
7: external terminal, 71: surface,
8: high void layer (inorganic porous layer),
11: positive electrode,
111: positive electrode metal foil (current collector foil) 112: positive electrode active material layer
12: negative electrode,
121: negative electrode metal foil (current collector foil) 122: negative electrode active material layer
91: bus bar member,
100: Power storage device.

Claims (3)

An electrode body having a positive electrode and a negative electrode as electrodes, and an electrolytic solution,
The electrode body has a separator substrate disposed between the positive electrode and the negative electrode,
The positive electrode and the negative electrode each have an active material layer containing active material particles,
The active material layer of the positive electrode and the active material layer of the negative electrode face each other via the separator base material,
The porosity of the active material layer of at least one of the electrodes is different between one and the other in the thickness direction, and is lower than the other at the one close to the separator substrate,
The energy storage device, wherein the electrode body has a higher porosity than the separator base material and further includes a high porosity layer disposed between the active material layer having a different porosity and the separator base material.   The power storage device according to claim 1, wherein the one porosity near the separator base material is 38% or more. Each of the positive electrode and the negative electrode has an active material layer in which the porosity is lower on the one side than on the other side in the thickness direction,
2. The high void layer is disposed both between the active material layer of the positive electrode and the separator substrate and between the active material layer of the negative electrode and the separator substrate. Or the power storage element according to 2.